In current electronic applications, discrete inductors, such as ferrite bead inductors, are often used to protect conductor lines against electromagnetic interference (EMI). These EMI filter ferrite bead inductors provide a resistance at high frequency that dissipates high frequency energy in the form of heat. Another application of ferrite inductors is output voltage smoothing for DC/DC-converter. Here, the ferrite inductor acts as a device with a high capability to store energy.
In both cases, ferrite inductors are widely used together with capacitors in order to provide efficient low pass characteristics. To date, ferrite inductors are manufactured as discrete SMD-devices in standard rectangular two terminal packages. For example, inductors are available in 0402 packages with a dimension corresponding to 1.0 mm by 0.5 mm. With mobile units like cellular phones and MP3-players becoming continuously smaller and requiring more power conversion functionality, the cost and size required for discrete inductors is becoming a limiting factor for further miniaturization.
Conventional discrete inductors are manufactured using a layered approach. A ferrite layer is provided on which a conductor is deposited, typically by printing. A second ferrite layer is deposited on the inductor and everything is baked together to enable a continuous magnetic flow in ferrite material. If more than one conductive layer is used, for example, to provide higher inductances, additional conductive and ferrite layers are stacked on one another and vias are provided to interconnect the conductive layers. The layered ferrite approach, however, is limited in the case of higher integration with other passive or active devices.